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Near-field assisted white-light interferometry (NFWLI). (a) Schematic of the construction of the NFWLI system by integrating a microsphere superlens into a Linnik white-light interferometer. The components are as follows: analyzer (A), quarter-waveplate (Q), beam splitter (BS), polarizing beam splitter (PBS), polarizer (P), Köhler illumination (KI), mirror (M), piezoelectric ceramic scanner (PZT), and objectives (O1 and O2). (b) The frames of images are recorded during PZT linear scanning along the light path, as shown by the red arrow. (c) Analyses of the recorded interference images for 3D morphology construction. (d) Constructed 3D super-resolution morphology by NFWLI.
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Recent developments in far-field fluorescent microscopy have enabled nanoscale imaging of biological entities by ingenious applications of fluorescent probes. For non-fluorescence applications, however, scanning probe microscopy still remains one of the most commonly used methods to “image” nanoscale features in all three dimensions, despite its li...
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... of NFWLI. Figure 1 shows the basic concept of a NFWLI system. The system integrates a micro- sphere superlens with a WLI based on the Linnik configuration (Fig. 1a). ...
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... of NFWLI. Figure 1 shows the basic concept of a NFWLI system. The system integrates a micro- sphere superlens with a WLI based on the Linnik configuration (Fig. 1a). The microsphere superlens magni- fies objects and forms virtual images by collecting and transforming near-field information into far-field for super-resolution imaging 1 . Before experiments, these microsphere superlenses are randomly dispersed onto sam- ples in air or in a water medium. The Linnik configuration was selected because ...
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... source was incorporated into the NFWLI system by a Köhler illumination (KI) system, in which 3D movable and variable aperture and field stops are used to adjust the illumination conditions. As the difference of optical paths in both arms is within the coherence length (1.16 μm) of the white-light source, interference fringes can be generated (Fig. 1b) 10 . The field-of-view (FOV) of the NFWLI system is limited by the FOV of the microsphere superlens, which linearly increases with increasing sphere diameter 21 , and by the aperture and field stops in the Köhler illumination system. As the piezoelectric ceramic (PZT) scanner scans in the reference arm direction, a series of image ...
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... by the FOV of the microsphere superlens, which linearly increases with increasing sphere diameter 21 , and by the aperture and field stops in the Köhler illumination system. As the piezoelectric ceramic (PZT) scanner scans in the reference arm direction, a series of image frames containing interference fringes are recorded by a high-speed camera (Fig. 1b). After the analyses of the recorded image frames (Fig. 1c), the 3D super-resolution morphology is constructed (Fig. ...
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... with increasing sphere diameter 21 , and by the aperture and field stops in the Köhler illumination system. As the piezoelectric ceramic (PZT) scanner scans in the reference arm direction, a series of image frames containing interference fringes are recorded by a high-speed camera (Fig. 1b). After the analyses of the recorded image frames (Fig. 1c), the 3D super-resolution morphology is constructed (Fig. ...
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... and field stops in the Köhler illumination system. As the piezoelectric ceramic (PZT) scanner scans in the reference arm direction, a series of image frames containing interference fringes are recorded by a high-speed camera (Fig. 1b). After the analyses of the recorded image frames (Fig. 1c), the 3D super-resolution morphology is constructed (Fig. ...
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... properties, i.e., the full-width at half-maximum (FWHM), intensity (|E| 2 ) and spatial positions (D), are influenced by different illumination conditions and diam- eters are shown in Fig. 6. The focus properties exhibit similar trends under the same illumination conditions as the microsphere diameter changes. Two boundary illumination conditions (Fig. 5a(iii-1,iii-2)) show the same focus properties (Fig. 6a), indicating that the illumination that does not transmit through the microsphere has negligible influence. As the light area (W1) increases, the focus FWHM decreases and the focus moves forward to the microsphere surface; however, the focus properties do not change when W1 approaches the ...
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... Simulated results show the relationship between the focus FWHM, position (D), the intensity of microspheres with diameters of (a) 10 μm, (b) 50 μm and (c) 70 μm, and the illumination size (W1/W2/W3). D represents the distance between the focus and microsphere apex, as shown in Fig. 5d(i). W1, W2 and W3 denote the illumination conditions shown in Fig. 5a(i,ii,iii-1,iii-2), respectively, and are defined in Fig. 5a. W00 is 14 μm, 70 μm and 100 μm in (a-c), respectively. W01 is 7 μm in (a). The definition of the abscissa corresponds to the legend for the different curves. 23 . The deletion of middle illumination decreases the scatter induced by propagation waves and weakens the obstruction on the ...
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... NFWLI system also provides a time-efficient method for 3D super-resolution imaging. For example, to image an 3.5 μm × 3.5 μm area while resolving sub-diffraction-limit features (e.g., as the images shown in Figs 1 and 3a), the NFWLI system will require approximately 25 s, whereas an AFM system requires approximately 17 min. In addition, this NFWLI image construction time could be further decreased through the development of more efficient algorithms and through the use of a higher-speed camera and scanner. ...
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... in NFWLI the microsphere superlens converts the evanescence waves into propagating waves 1,21,28 . and constructs the phase information along the vertical direction from the evanescent waves. The converted propagating light containing phase information interferes with the reference light after transmission through the analyzer, as shown in Fig. 1a. Thus, the interference occurs in the far-field, which is similar to the experi- ments of Carniglia and Mandel 26 and Cortes et al. 29 , i.e., the evanescent waves exist in the light beam but do not directly participate in the interference. But the original information of the sample was completely perturbed in the experiments of Cortes ...
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... polarizing beam splitter, polarizer and mirror used to assemble the NFWLI system were obtained from Thorlabs. The NFWLI system was fitted with a pair of 50× objectives (NA = 0.6, Nikon Plan EPI ELWD) and a high-speed scientific complementary metal oxide semiconductor (sCMOS) camera (PCO, Edge 5.5). The interferometric light path shown in Fig. 1 was coupled with the high-speed camera by a body tube (12× UltraZoom, 1-50503AD, Navitar). The mirror in the reference arm was driven by a piezo translation stage (NPX25-105, nPoint). The NFWLI sys- tem was illuminated by an intensity-controllable light source (C-HGFI, Nikon), and the middle wavelength was confined to approximately 550 ...
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Nanoscale materials are nowadays widely used in many different modern technologies. Special attention is thus required for their characterization in order to optimize fabrication processes. However, current characterization systems which can achieve nanometric resolution over a large area and in three dimensions are few. Classical optical microscop...
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... The smaller the diameter, the better is the lateral resolution but the smaller the field of view 37,38 . Different solutions exist for manipulating the microsphere, for example using a micropipette 39 , an AFM cantilever 28,40 or by a support attached to the objective 27,29,34 . They also allow an increase in the field of view thanks to scanning and stitching techniques, making the use of smaller microspheres possible to maintain a high resolution and avoid the tradeoff between the field of view and the gain in resolution, although at the cost of acquisition time. ...
... Microsphere-assisted microscopy also presents the advantage of being able to be used with several optical microscopy techniques such as dark-field microscopy 41 , fluorescence microscopy 24 , confocal microscopy 42 , and digital holographic microscopy 43 . Microspheres have also been successfully combined with interference microscopy to benefit both from the nanometric axial sensitivity and improved lateral resolution in nanometric topographic measurement, such as that of 3D sub-diffraction sized elements 40,[44][45][46][47][48] . Recently, microspheres have also been used as a photonic nanojet generator to perform spectral measurements with a reduced lateral spot size of 210 nm 49 , by combining a microsphere with a reflection microscope and fibered spectrometer. ...
... However, if smaller microspheres are used to improve the lateral resolution, one disadvantage is that the field of view is smaller. To overcome the trade-off between the lateral resolution and the field of view, one strategy could be to combine the technique described in this paper with a lateral scan of the microsphere over the sample 27,40 , at the cost of longer acquisition and processing times. Another strategy to increase the field of view would be to spatially parallelise the acquisitions by replacing the microsphere with a matrix of microspheres 51 , although such a matrix is difficult to produce. ...
The characterisation of novel materials presents a challenge that requires new and original developments. To face some of these demands for making measurements at the nanoscale, a new microsphere-assisted white light interference nanoscope performing local reflectance mapping is presented. This technique presents the advantages of being non-destructive, full-field and label-free. A 145 μm diameter microsphere, glued to the end of an optical fiber, is inserted inside the white light interference microscope to improve the lateral resolution from 940 nm to 520 nm. The acquisition and the Fourier transform processing of a stack of interference images superimposed on the virtual image produced by the microsphere allows the extraction of the local reflectance over a wavelength range of 460 nm to 900 nm and a field of view of 8 μm in diameter. The enhancement in the lateral resolution of the reflectance is demonstrated through the spectral distinction of neighboring ripples on a laser-textured colored stainless-steel sample that cannot be resolved without the microsphere, on regions with a surface of 279 × 279 nm² horizontally spaced 279 nm apart. Future improvements could potentially lead to a lateral resolution of reflectance measurement over a 100 nm diameter area in air, paving the way to sub-diffraction reflectance mapping.
... A comprehensive review of the microsphere superlens technique, including its fundamentals and applications, can be found in our previous publication [6]. Key advancements in photonic nanojets mainly pursue two research directions: first, focusing laser beams onto the sample surface to achieve nanopatterning with sub-100 nm feature sizes, and secondly, manipulating light reflected from the sample surface, forming the foundation of super-resolution optical imaging to observe subwavelength objects and structures with resolution as fine as 45 nm [10,11]. ...
... Previous publications have demonstrated 80 nm resolution in laser nanopatterning [12] and 45-50 nm resolution in nanoimaging [10,13], alongside other notable developments [14]. ...
In this paper, we present a unique multi-functional super-resolution instrument, the SuperNANO system, which integrates real-time super-resolution imaging with direct laser nanofabrication capabilities. Central to the functionality of the SuperNANO system is its capacity for simultaneous nanoimaging and nanopatterning, enabling the creation of anti-counterfeiting markings and precision cutting with exceptional accuracy. The SuperNANO system, featuring a unibody superlens objective, achieves a resolution ranging from 50 to 320 nm. We showcase the instrument’s versatility through its application in generating high-security anti-counterfeiting features on an aluminum film. These ‘invisible’ security features, which are nanoscale in dimension, can be crafted with arbitrary shapes at designated locations. Moreover, the system’s precision is further evidenced by its ability to cut silver nanowires to a minimum width of 50 nm. The integrated imaging and fabricating functions of the SuperNANO make it a pivotal tool for a variety of applications, including nanotrapping, sensing, cutting, welding, drilling, signal enhancement, detection, and nanoscale laser treatment.
... Over the past few years, superlenses made from dielectric materials, especially in spherical shapes, have emerged as a powerful platform for challenging the diffraction limit [4][5][6]. These advancements mainly pursue two research directions: firstly, focusing laser beams onto the sample surface to achieve nanopatterning with sub-100 nm feature sizes, and secondly, manipulating light reflected from the sample surface, forming the foundation of super-resolution optical imaging to observe subwavelength objects and structures with resolution as fine as 45 nm [7,8]. Previous publications have demonstrated 80-nmresolution in laser nanopatterning [9] and 45-50 nm resolution in nanoimaging [7,10], alongside other notable developments [11]. ...
... These advancements mainly pursue two research directions: firstly, focusing laser beams onto the sample surface to achieve nanopatterning with sub-100 nm feature sizes, and secondly, manipulating light reflected from the sample surface, forming the foundation of super-resolution optical imaging to observe subwavelength objects and structures with resolution as fine as 45 nm [7,8]. Previous publications have demonstrated 80-nmresolution in laser nanopatterning [9] and 45-50 nm resolution in nanoimaging [7,10], alongside other notable developments [11]. ...
In this paper, we present a unique multi-functional super-resolution instrument, the SuperNANO system, which integrates real-time super-resolution imaging with direct laser nanofabrication capabilities. Central to the func-tionality of the SuperNANO system is its capacity for simultaneous nanoimaging and nanopatterning, enabling the creation of anti-counterfeiting markings and precision cutting with exceptional accuracy. The SuperNANO system, featuring a unibody superlens objective, achieves a resolution ranging from 50 to 320 nm. We showcase the instrument's versatility through its application in generating high-security anti-counterfeiting features on an aluminum film. These 'invisible' security features, which are nanoscale in dimension, can be crafted with arbi-trary shapes at designated locations. Moreover, the system's precision is further evidenced by its ability to cut silver nanowires to a minimum width of 50 nm. The integrated imaging and fabricating functions of the Su-perNANO make it a pivotal tool for a variety of applications, including nano trapping, sensing, cutting, weld-ing, drilling, signal enhancement, detection, and nano laser treatment.
... Many improvements of this technology have been demonstrated; among them is the use of high-index microspheres in liquids [5,6] or in movable plastic films [4] and the implementation of scanning by attaching the microsphere to an AFM cantilever [7,8]. Microspheres can be incorporated into confocal imaging [9,10], interferometry [11,12], or digital holography [13][14][15]. Microsphere-assisted microscopy is one example of rapidly developing techniques of label-free super-resolution imaging [16]. ...
Exploring the performance of label-free imaging relies heavily on adequate physical models and accurate numerical simulations. A particularly challenging situation is imaging through contact microspheres, which have demonstrated resolution values exceeding the diffraction limit. Here an ab initio modeling of microsphere-assisted imaging is reported and its results are analyzed. The key part of modeling is solving the light scattering problem, which requires handling a rather large computational domain and broad angle illumination made up of multiple mutually incoherent plane waves. To account for plane wave incidence, two simulation approaches are developed that differ only by boundary conditions–quasiperiodic and absorbing. The algorithms to find images in both approaches are discussed and the simulation results are compared for free space and microsphere-assisted imaging. It is shown that while the super-resolution in microsphere-assisted imaging can be demonstrated using both approaches, the latter allows a large reduction in the computational resources. This significantly extends the capability of the simulations, enabling a rigorous exploration of novel imaging regimes.
... They conducted a theoretical analysis of the imaging phenomenon using the characteristics of the electric field vector and photon nanojets. In 2016, Feifei Wang et al. [11] investigated the effect of illumination modes on the super-resolution of microspheres while implementing three-dimensional super-resolution detection with microsphere-assisted white light interferometry. They also proposed a non-invasive microsphere scanning superlens microscope with temporal efficiency. ...
Conventional optical microscopes are only able to resolve objects down to a size of approximately 200 nm due to optical diffraction limits. The rapid development of nanotechnology has increased the demand for greater imaging resolution, with a need to break through those diffraction limits. Among super-resolution techniques, microsphere imaging has emerged as a strong contender, offering low cost, simple operation, and high resolution, especially in the fields of nanodevices, biomedicine, and semiconductors. However, this technology is still in its infancy, with an inadequate understanding of the underlying principles and the technology’s limited field of view. This paper comprehensively summarizes the status of current research, the advantages and disadvantages of the basic principles and methods of microsphere imaging, the materials and preparation processes, microsphere manipulation methods, and applications. The paper also summarizes future development trends.
... This is important to prevent the accumulation of photoresist on the microsphere. Current depth-measurement principles investigated by other works include the application of coherence scanning interferometry [16][17][18][19] , digital holography 20, 21 and scatterometry 22 . Although these principles could demonstrate the extension of the effective NA, they are not very suitable for the active control of the height of the microsphere above the photoresist. ...
The integration of microspheres within the instruments of optical metrology and mask-less lithography could
already show a significant enhancement of their lateral resolution. Exposing complex large structures exploiting
this high resolution requires the lateral movement of the microsphere over the substrate. Challenging remains
the accurate lateral and axial positioning of the microsphere ensuring the constant exposure conditions at every
point. Preserving the advantage of optical instruments to not actually contact the specimen, the microsphere
must be kept at a nanometer-close, yet constant distance from the surface. Here, we introduce the, to our
best knowledge, novel approach to combine the principle of the differential confocal microscope with a scanning
microsphere. This produces a differential signal towards the surface allowing a nanometer-sensitive and fast
control of the axial position of the microsphere above the substrate. In preliminary experiments we show the
repeatable pick-up of microspheres and their precise lateral scanning using a nanopositioning and nanomeasuring
machine as well as axial depth responses and differential signals from the realized microsphere assisted differential
confocal probe.
... Based on our previous work 12, 36 , a non-invasive, highthroughput, environmentally compatible optical SSUM system was developed and the composition and performance characteristics of the systems are shown in the Supplementary Fig. S3. Figure 1 shows the schematic construction of the SSUM, which can be used for large-area, super-resolution imaging and data acquisition. The optical super-resolution imaging system consists of an AFM, a commercially available cantilever (TESP probe, Bruker), a 57-μm-diameter BTG microsphere lens (Cospheric) and a 100× objective lens (Nikon LU Plan EPI ELWD). ...
Scanning electron microscopy (SEM) enables nanoscale imaging but requires vacuum environments and coating samples with conductive films. We present a deep learning approach to transform optical super-resolution (OSR) microscopy images into SEM-like images without these limitations. Our custom scanning superlens microscopy system acquires OSR images down to ~80 nm without coatings or vacuum. A generative adversarial network (GAN) model is trained on paired OSR and SEM images to learn the mapping between domains. The model is then used to transform previously unseen OSR test images. Quantitative analysis shows the reconstructed images achieve a mean peak signal-to-noise ratio 0.74 dB higher than the input OSR images. Qualitative assessment further demonstrates the model's ability to generate results with high structural detail. This technique overcomes key SEM constraints while preserving nanoscale resolution, promising wide applicability for challenges such as chip-level defect detection and biological sample analysis where coating or vacuum requirements pose obstacles.
... This effect can probably be explained by the magnification induced by the sphere leading to a larger measured period length, which requires a lower evaluation wavelength. For more explanation and a detailed view on the effects in the 3D spatial frequency domain, we refer to Hüser et al. 15,40,48 . ...
... The figure is not drawn to scale to enhance comprehensibility. Adapted from Ref.40. Copyright 2023 Author(s), licensed under a Creative Commons Attribution license. ...
... F. Wang proposed three-dimensional superresolution microscopy via a microsphere superlens based on Linnik white light interferometry method. They used two objectives and BaTiO3 microspheres randomly placed on the samples, realizing super-resolution 3D reconstruction with a lateral resolution of 50 nm and axial resolution of 10 nm [29]. Later on, I. Kassamakov and P. Lehmann also demonstrated the super-resolution 3D optical profiling capability of the microsphere-assisted interferometry method, presenting the constructed results on Blu-ray Disc and other grating structures [30][31][32]. ...
With the rapid development of the information era and super-precision fabrication technology, micro/nano technology has already become one of the most important modern scientific directions. To quantitatively characterize the defects, uniformity, quality and performances of micro/ nano devices, three-dimensional topography measurement plays a key role and has become increasingly 6important. In this paper, we proposed a microsphere-aided Mirau-based broadband light interferometry method to achieve super-resolution 3D topography reconstruction. We numerically and experimentally demonstrated that dielectric microspheres, which can introduce the phenomenon of photonic nanojet, could break the optical diffraction limit and achieve super-resolution microscopy under white light illumination. The subwavelength samples, which could not be detected by conventional microscopy, were clearly visualized by the proposed microsphere-aided microscopy. Furthermore, we applied the advanced Stoilov five-step phase shifting method to reconstruct the 3D topography. The experiment results demonstrated that our proposed microsphere-aided broadband light interferometry method could successfully reconstruct the 3D shape of nanoscale cylinders with the feature size of 228 nm and height of 150 nm with an error of 2%. As microsphere is a low-cost, easy-to-use, and super-resolution imaging method, it bears great potential to be widely applied in both scientific and industrial areas. We believe that our proposed super-resolution three-dimensional topography measurement using microsphere-aided broadband light interferometry will be of great interests in semiconductor, material, laser eavesdropping, extreme fabrication and biomedical applications.
... Recently, Wu and Hong achieved tunable magnification at 2.8× to 10.3× in imaging specimens using MCL under a non-contact mode and further increased the FOV by scanning working mode [15]. Additionally, a microsphere lens can be further integrated with mechanical scanning systems (such as atomic force microscope cantilevers [16,17]) or optical trapping [18] to accurately control the imaging position and significantly expand the FOV in super-resolution imaging of large-area samples. ...
In this paper, a cascaded microsphere compound lens (CMCL) is introduced, in which a 20-µm-diameter barium titanate glass (BTG) primary microsphere and a 250-nm-diameter or 200-nm-diameter polystyrene (PS) secondary microsphere array constitute CMCL1 and CMCL2, respectively. The field of view (FOV) depends on the size of the BTG microsphere, while the waist of the photon nanojet (PNJ) can be adjusted by the size of the PS microsphere. The narrower the waist of the PNJ, the higher the imaging resolution. In the experiment, a 200-nm-diameter hexagonally close-packed PS nanoparticle array is successfully observed by the CMCL with a high magnification of ∼ 11.6 × and a FOV of {\sim} {14}\;{\unicode{x00B5}{\rm m}} ∼ 14 µ m , while the single BTG microsphere is incapable of observing the array. The point spread function is used to quantify the resolution of the CMCL. A well-designed CMCL can improve the imaging performances of a microsphere-assisted microscope.